EP2171787A1

EP2171787A1 - Apparatus for recirculation of a cathode gas in a fuel cell arrangement, method for shutting down a fuel cell apparatus with the fuel cell arrangement

Info

Publication number: EP2171787A1
Application number: EP08773516A
Authority: EP
Inventors: Andreas Knoop
Original assignee: Daimler AG; Ford Global Technologies LLC
Current assignee: Mercedes Benz Group AG
Priority date: 2007-07-26
Filing date: 2008-06-19
Publication date: 2010-04-07
Also published as: DE102007035056A1; JP2010534902A; WO2009012854A1; US8691452B2; US20110045368A1

Abstract

The invention is based on the object of providing an apparatus for recirculation of a cathode gas in a fuel cell arrangement, which apparatus allows the fuel cell arrangement to be shut down safely, and proposing a corresponding method for shutting down the fuel cell apparatus. An apparatus (2) for recirculation of a cathode gas in a fuel cell arrangement (3) having a cathode gas supply (7) for supplying the cathode gas to a cathode area (5) in the fuel cell arrangement (3), having a cathode gas outlet (9) for carrying the partially consumed cathode gas out of the cathode area (5), having a recirculation line (11) for recirculation of the partially consumed cathode gas from a junction point (10) in the cathode gas outlet (9) into a supply point (12) in the cathode gas supply (7), is characterized by a blocking apparatus (15, 16) which is designed to block the cathode gas supply (7) in the flow direction upstream of the supply point (12) and to block the cathode gas outlet in the flow direction downstream from the junction point (10), such that a closed circuit for the partially consumed cathode gas is formed when the blocking apparatus (15, 16) is closed.

Description

Apparatus for recirculation of a cathode gas in a fuel cell arrangement, method for shutting down a fuel cell apparatus with the fuel cell arrangement

The invention relates to an apparatus for recirculation of a cathode gas in a fuel cell arrangement having a cathode gas supply for supplying the cathode gas to a cathode area in the fuel cell arrangement, having a cathode gas outlet for carrying the partially consumed cathode gas out of the cathode area, and having a recirculation guide for recirculation of the partially consumed cathode gas from a junction point in the cathode gas outlet into a supply point in the cathode gas supply, and to a method for shutting down a fuel cell apparatus which is formed from the apparatus and the fuel cell arrangement.

Fuel cell apparatuses are used to convert chemical energy to electrical energy, with a fuel, for example hydrogen, being reacted with an oxidant, for example environmental air, in an electrochemical process. Fuel cell apparatuses such as these are on the one hand used in a stationary form, and on the other hand, as mobile generators, they provide the capability to supply power to a drive train in a vehicle.

One technical requirement is to cope with the demanding electrochemical process, on the one hand with the reaction of the fuel being economic and on the other hand with the fuel cell apparatus being operated permanently and operationally safely.

By way of example, the document DE 102 03 029 Al discloses a fuel cell apparatus having a specific configuration of an apparatus for supplying a medium containing oxygen into a cathode area of a fuel cell in the fuel cell apparatus. This document proposes that cathode gas which has been partially consumed in the electrochemical process be recirculated, starting from a cathode outlet, be mixed with fresh cathode gas and then be supplied to the cathode input again. The particular advantages of this procedure are that the water which is created during the electrochemical process is fed back through the partially consumed cathode gas and is used to moisturize the sensitive intermediate membrane between the cathode area and the anode area. A controllable restriction apparatus is arranged in a recirculation line, in order to control the proportion of the recirculated, partially consumed cathode gas.

Laid-Open Specification DE 102 047 87 Al relates to a flap valve for fuel sets, which is intended to be used in particular in the field of fuel supply, that is to say in the anode gas circuit. The flap valve comprises a flap which is arranged within a flow channel and can be pivoted via a moveable shaft, and a seal which is connected to a channel wall and has a so-called pressure pocket.

Another valve apparatus in the form of a bypass valve is known from the document DE 103 25 196 B3, which is in the form of a switching flap and has a flap plate which can be pivoted by means of a shaft which is arranged outside the flap plate. In order to improve the valve sealing, a sealing element is provided, which is arranged on the circumference of the flap plate and has at least two sealing lips which run parallel to one another. The field of the application is considered to be fuel cell apparatuses, in particular in the area of the anode gas circuit.

Laid-Open Specification DE 103 28 246 Al relates to a further valve which has a valve body which is mounted by means of a shaft that is passed through. A sealing column is fitted on the valve body in order to seal the shaft, as well as a sealing strip which runs around the edge of the circumference, with the sealing strip being interrupted in the circumferential direction in order to allow the shaft to pass through, and to allow the sealing column to be attached.

The fuel cell apparatus according to the document DE 102 03 029 Al is regarded as the closest prior art.

The invention is based on the object of providing an apparatus for recirculation of a cathode gas in a fuel cell arrangement, which apparatus allows the fuel cell arrangement to be shut down safely, and of proposing a corresponding method for shutting down a fuel cell apparatus which is formed from the apparatus and the fuel cell arrangement.

This object is achieved by an apparatus having the features of Claim 1, by a fuel cell apparatus having the features of Claim 13, and by a method having the features of Claim 14. Preferred or advantageous embodiments of the invention will become evident from the dependent claims, from the following description and from the attached figures.

According to the invention, an apparatus is proposed for recirculation of a cathode gas in a fuel cell arrangement, which apparatus is probably suitable and/or designed for use as a mobile energy source, in particular in a vehicle. The fuel cell arrangement preferably has a multiplicity of fuel cells, in particular more than 100, which are connected in series, for example, in order to produce an adequate output voltage. The fuel cells each have a cathode area and an anode area which are separated from one another by a proton exchange membrane. The totality of the cathode areas and of the anode areas, respectively, is referred to in brief in the following text as the cathode area and anode area respectively.

The apparatus has a cathode gas supply for supplying the cathode gas, in particular oxygen or environmental air, to the cathode area in the fuel cell arrangement and, for example, is in the form of a supply line or a tube.

For carrying the partially consumed cathode gas out of the cathode area, the apparatus has a cathode gas outlet which, for example, is also in the form of a line or a tube.

Furthermore, the apparatus has a recirculation guide for recirculation of the partially consumed cathode gas from a junction point in the cathode gas outlet into a supply point in the cathode gas supply. The cathode gas outlet is therefore split at a junction point in the flow direction downstream from the cathode area, with a first flow element being emitted, for example, into the environment and a second flow element being passed via the recirculation guide to the supply point in the cathode gas supply. During normal operation, the partially consumed cathode gas is mixed with fresh cathode gas, for example from the environment, at the supply point, and is passed to the cathode area again. According to the invention, a blocking apparatus is proposed which is designed to block the cathode gas supply in a gas- tight manner upstream of the supply point and to block the cathode gas outlet downstream from the junction point. A closed circuit for the partially consumed cathode gas is formed when the blocking apparatus is closed, with the partially consumed cathode gas being passed from the cathode area via the junction point and via the supply point into the cathode area again, with no fresh cathode gas being added.

One consideration on which the invention is based is in this case that the life of fuel cells, in particular for automobile applications, is reduced inter alia by corrosion processes. Although corrosion processes such as these also take place during operation, they occur in particular when the fuel cell arrangement is in the rest state. For the purposes of the invention, it is now proposed that the recirculation arrangement for the cathode gas in the fuel cell arrangement be modified such that it is possible to circulate the partially consumed cathode gas in a closed circuit through the cathode area during the process of switching off the fuel cell arrangement. In this way, the oxygen which still remains in the partially consumed cathode gas is dissipated thus resulting in oxygen depletion and nitrogen enrichment (as well as other gases) in the partially consumed cathode gas. This measure and the procedure result in the oxygen being extracted from the cathode area and from the cathode gas system, thus preventing or at least reducing the corrosion processes associated with it. A further possible advantage is that no oxygen or little oxygen can diffuse into the anode area during the rest phase of the fuel cell arrangement, therefore in this way also making it possible to effectively prevent corrosion processes in the anode area of the fuel cell arrangement while it is shut down.

In one preferred embodiment of the invention, the apparatus has a continuous-flow machine which is designed to recirculate the partially consumed cathode gas when the blocking apparatus is closed. The continuous-flow machine is therefore arranged and/or connected for flow purposes such that it can move the partially consumed cathode gas in the closed circuit for the partially consumed cathode gas. The continuous-flow machine is preferably also designed to compress the cathode gas when the blocking apparatus is open, so that it carries out a dual function, therefore saving components .

In particular the continuous-flow machine is intended to be a turbocharger (ETC) which is or can be electrically driven, although it may also be in the form of a volumetric compressor, for example a screw-type compressor or Roots compressor.

In general, this may also relate to an impulse exchange machine. This embodiment once again underscores the inventive concept of circulating the partially consumed cathode gas when the blocking apparatus is closed, in order to reduce oxygen content.

In one preferred implementation of the invention, the apparatus has a control apparatus, which is in the form of programming and/or circuitry, and is designed to block the blocking apparatus and at the same time to activate the continuous-flow machine, or to keep it activated in a switched-off operating mode. It is also possible for the switched-off operating mode to occur in the course of maintenance, repair or the like.

The control apparatus may be in the form of a local control or a part of a higher-level control system. The control apparatus preferably allows a plurality of operating modes, with the switched-off operating mode representing one possible operating mode.

The control apparatus is preferably in the form of programming and/or circuitry such that the switched-off operating mode is maintained for a defined time interval and/or as a function of the remaining oxygen content in the partially consumed cathode gas. A time interval determined and/or calculated from an empirical value is entered by a user for a defined time interval. For example, appropriate sensors, in particular oxygen sensors, are provided in the apparatus for closed-loop or open-loop control as a function of the remaining oxygen content in the partially consumed cathode gas, with the recirculation being deactivated when a limit value is undershot.

Alternatively, the voltage of the fuel cell can also be used as a switch-off criterion since, when no oxygen is present, no voltage is produced either.

In one preferred design implementation, the blocking apparatus comprises one or more valves or restrictors which is or are designed and/or arranged in order to block the cathode gas outlet and/or the cathode gas supply. The valves may be designed, for example, as in the initially cited documents DE 102 047 87 Al, DE 103 25 196 B3 or DE 103 28 246 Al, whose disclosure content relating to the physical form is hereby included in its entirety in the present disclosure, by reference .

In one preferred development of the invention, the valve or valves and/or the restrictor or restrictors are/is designed to be self-latching, in particular self-latching in the open and/or closed state. Particularly from the point of view of FMEA aspects, it is in this case preferable for the valves and/or restrictors to be open when no current is applied to an operation and to be closed when no current is flowing after the fuel cell arrangement has been switched off, in order to prevent the ingress of fresh cathode gas or environmental air. One possible implementation of the self- latching valves or restrictors is for these devices to be driven via a worm drive, in particular a self-locking worm drive .

Stimulated by the requirement to use a small number of active components, it is proposed that all the valves and/or restrictors of the blocking apparatus preferably be driven by a common actuator. This can be achieved, for example, by means of a linkage or a common shaft or a Bowden cable, in order to mechanically couple the valves and restrictors. As an alternative to this, each valve and each restrictor can also be allocated a separate actuator.

At least one of the restrictors in the blocking apparatus preferably has a restrictor valve and optionally a restrictor valve housing, with the restrictor valve being sealed with respect to the restrictor valve housing and the gas-carrying lines by means of an elastic sealing system. In this case, on the one hand, it is possible to seal the restrictor by means of a circumferential seal on a sealing disc of the restrictor valve and/or for the restrictor valve housing to be rubber- coated internally, in particular in those areas on which the restrictor valve rests in the closed state.

A modification of the invention proposes that the blocking apparatus has a pressure maintenance mechanism, in particular a pressure maintenance valve, preferably in the form of a restrictor or control valve and/or a proportional valve, which carries out the function of blocking the cathode gas outlet. This allows a pressure maintenance mechanism which already exists on the cathode outlet side in the fuel cell apparatus to be modified in a simple manner in order to integrate the additional functionality of blocking the gas flow. In this embodiment, only one blocking device is required to block the cathode gas supply.

A further subject matter of the invention relates to a fuel cell apparatus designed in particular for a vehicle, which apparatus comprises the fuel cell arrangement and the apparatus for recirculation according to one of the preceding claims and/or as has been described above.

A next subject matter of the invention relates to a method for switching off or shutting down a fuel cell apparatus according to Claim 14, with, when the fuel cell apparatus is being switched off, the blocking apparatus being switched such that the partially consumed gas circulates in a closed circuit through the cathode area.

For open-loop and/or closed-loop control purposes, the partially consumed cathode gas is preferably circulated until the oxygen in the cathode gas is consumed, or has fallen below a limit value. Further features, advantages and effects of the inventions result from the following description of one preferred exemplary embodiment of the invention, and from the attached figure, in which:

Figure 1 shows a schematic block diagram of a fuel cell apparatus, as a first exemplary embodiment of the invention.

Figure 1 shows a schematic illustration of a fuel cell apparatus 1 having an apparatus for recirculation 2 as one exemplary embodiment of the invention.

The fuel cell apparatus 1 comprises a fuel cell stack 3 which has a plurality of fuel cells, but at least one fuel cell. The fuel cell stack 3 comprises an anode area 4 and a cathode area 5, which are separated from one another by means of a membrane 6 (PEM) . In order to supply the cathode area 5, the fuel cell apparatus 1 has a cathode gas supply 7 whose input is connected to the environment or to an oxygen tank, and whose output opens in the cathode area 5. Originating from the environment or the oxygen tank, an oxidant mass flow is passed via the cathode gas supply 7 into the cathode area 5, in order to carry out an electrochemical reaction there, in a known manner, with a fuel in the anode area 4 in order to produce electrical energy. A compressor 8 is arranged in the cathode gas supply 7 in order to compress the supplied gas, and is in the form of a volumetric or impulse exchange machine, but particularly preferably a continuous-flow machine (turbocharger or turbocompressor) . In particular, the gas is compressed using the dynamic princip Ie, in which energy transmission preferably takes place via an impeller with blades, through which flow passes continuously. The partially consumed cathode gas which is carried out of the cathode area 5 after the electrochemical reaction is at least partially dissipated into the environment via a cathode gas outlet 9 originating from the cathode area 5.

In order to recirculate the partially consumed cathode gas, the outlet line 9 has a junction point 10 downstream from the cathode area 5, to which junction point 10 a recirculation guide 11 is connected. The recirculation guide 11 connects the junction point 10 to a supply point 12 in the cathode gas supply 7. The supply point 12 is arranged upstream from the continuous-flow machine 8 in the flow direction, that is to say on the suction side of the continuous-flow machine. A portion of the partially consumed cathode gas is therefore tapped off through the recirculation guide 11 and is added to the fresh cathode gas fl ow, with this mixture being compressed as the working gas in the continuous-flow machine 8 and finally being supplied to the cathode area 5.

During normal operation of the fuel cell apparatus 1, the recirculation guide 11 is provided with closed-loop or open- loop control via a valve 13 as a function of the required moisture or the mass flow of the oxidant, for example, the recirculation apparatus 2 is switched when the fuel cell apparatus 1 is being shut down or switched off such that the partially consumed cathode gas is circulated in a closed circuit through the cathode area 5 without fresh cathode gas being supplied, in order to completely or virtually completely dissipate the oxygen remaining in the partially consumed cathode gas . In order to carry out the switching process, the fuel cell apparatus 1 has a control apparatus 14 which is designed to control an input restrictor 15 and an output restrictor 16, as well as the continuous-flow machine 8. The input restrictor 15 is arranged in the flow upstream of the supply point 12 in the cathode gas supply 7 and makes it possible to block the cathode gas supply 7 in a gas-tight manner such that no fresh cathode gas can be supplied in the direction of the cathode area 5. The output restrictor 16 is arranged in the flow downstream from the junction point 10 and allows the cathode gas outlet to be blocked in a gas- tight manner, so that no fresh cathode gas or environmental air can enter in the direction of the cathode area 5 from this side either.

The input and/or output restrictors 15, 16 each, for example, have a restrictor valve which is provided with an elastic seal which ensures adequate, gas-tight sealing of the components. For example, one such restrictor valve has a circumferential seal. Alternatively or additionally, the input and/or output restrictors 15, 16 have a restrictor valve housing which is provided with a rubber coating for sealing purposes in the contact area with the restrictor valve.

Each of the restrictors 15, 16 may have its own actuator for drive purposes, or alternatively and advantageously a common actuator can be provided for control purposes - since these two restrictors are each switched at the same time - and passes the control movements to the restrictors 15, 16 by cables, linkages or the like.

Once a switched-off operating mode has been activated, the control apparatus 14 closes the input restrictor 15 and the output restrictor 16 and activates the continuous-flow machine 8, resulting in recirculation of the partially consumed cathode gas via the cathode area 5 and the recirculation guide 11. This recirculation is continued until the oxygen in the partially consumed cathode or recirculation gas has been adequately dissipated by electrochemical or catalytic processes. The control apparatus 14 then switches off the continuous-flow machine 8.

This switching-off procedure ensures that no oxygen or only a small residual amount of oxygen remains in the cathode-side area of the fuel cell apparatus 1. Furthermore, this ensures that no oxygen can diffuse from the cathode area 5 into the anode area 4, thus also resulting in an oxygen-free or low- oxygen area there. In consequence, the fuel cell apparatus 1 is switched by the proposed apparatus and the proposed method to have little or no oxygen, so that corrosion processes are prevented, or are at least greatly slowed down, and the life of the fuel cell apparatus 1 and in particular of the membrane 6 can be considerably lengthened.

Claims

Patent Claims

1. Apparatus (2) for recirculation of a cathode gas in a fuel cell arrangement (3)

having a cathode gas supply (7) for supplying the cathode gas to a cathode area (5) in the fuel cell arrangement (3),

having a cathode gas outlet (9) for carrying the partially consumed cathode gas out of the cathode area (5) ,

having a recirculation guide (11) for recirculation of the partially consumed cathode gas from a junction point (10) in the cathode gas outlet (9) into a supply point (12) in the cathode gas supply (7) ,

characterized by

a blocking apparatus (15, 16) which is designed to block the cathode gas supply (7) in the flow direction upstream of the supply point (12) and to block the cathode gas outlet in the flow direction downstream from the junction point (10) , such that a closed circuit for the partially consumed cathode gas is formed when the blocking apparatus (15, 16) is closed.

2. Apparatus (2) according to Claim 1, characterized by a continuous-flow machine (8) which is designed to recirculate the partially consumed cathode gas when the blocking apparatus (15, 16) is closed.

3. Apparatus (2) according to Claim 2, characterized in that the continuous-flow machine is a turbocharger (ETC) which is or can be electrically driven.

4. Apparatus (2) according to Claim 2, characterized in that the continuous-flow machine is in the form of a volumetric compressor, in particular a screw-type compressor or Roots compressor.

5. Apparatus (2) according to one of Claims 1 to 4, characterized by a control apparatus (14) which is designed to block the blocking apparatus (15, 16) and to activate the continuous-flow machine (8) in a switched-off operating mode.

6. Apparatus (2) according to Claim 5, characterized in that the control apparatus (14) is designed to maintain the switched-off operating mode for a defined time interval and/or as a function of the remaining oxygen content in the partially consumed cathode gas.

7. Apparatus (2) according to one of the preceding claims, characterized in that the blocking apparatus (15, 16) comprises one or more valves and/or restrictors in order to block the cathode gas outlet and/or the cathode gas supply.

8. Apparatus (2) according to Claim 7, characterized in that the valve or valves and/or restrictor or restrictors (15, 16) are designed to be self-latching.

9. Apparatus (2) according to Claim 8, characterized in that the valve or valves and/or restrictor or restrictors can be driven via a worm drive.

10. Apparatus (2) according to one of Claims 7 to 9, characterized in that all the valves and/or all the restrictors of the blocking apparatus (15, 16) are driven by a common actuator.

11. Apparatus (2) according to one of the preceding Claims 7 to 10, characterized in that at least one of the restrictors (15, 16) has a restrictor valve, with the restrictor being sealed by a circumferential seal on the sealing disc of the restrictor valve and/or via an internally rubber-coated restrictor valve housing.

12. Apparatus (2) according to one of the preceding claims, characterized in that the blocking apparatus (15, 16) has a pressure maintenance mechanism which is arranged in the cathode gas outlet (9) , in the flow direction downstream from the junction point (10), and is designed to block the cathode gas outlet (9) .

13. Fuel cell apparatus (1), in particular for a vehicle, having an apparatus for recirculation (2) according to one of the preceding claims.

14. Method for switching off or shutting down a fuel cell apparatus (1) according to Claim 11, characterized in that, when the fuel cell apparatus (1) is being switched off, the blocking apparatus (15, 16) is switched such that the partially consumed gas circulates in a closed circuit through the cathode area (5) .

15. Method according to Claim 14, characterized in that the partially consumed cathode gas is circulated until the residual oxygen in the cathode gas is consumed, or has fallen below a limit value.